1. Field of the Invention
The invention relates to a process for the production of superconducting fiber bundles where in a CVD (chemical vapor deposition) reactor niobium oxycarbonitride of the general formula NbC.sub.x N.sub.y O.sub.z (x, y, x, .gtoreq.0 and x+y+z.ltoreq.1) is deposited on the support fiber by means of chemical deposition from the gaseous phase by reaction of niobium chloride and carbon and nitrogen compounds.
2. Description of the Prior Art
In the continued development of energy technology with respect to nuclear fusion and superconducting generators, of traffic technology (e.g. magnetic suspension train), of environment technology (e.g. desulfurization of coal) and of high-energy physics, strong-field magnets are needed, which can be produced only on the basis of superconductors.
A new promising superconduction material is NbC.sub.x N.sub.y O.sub.z (x,y,z.gtoreq.0 and x+y+z+.ltoreq.1) which, applied on support fibers of a fiber bundle (consisting for example of several thousand fibers of a diameter of about 5 to 7 .mu.m), can be used as fiber conductor. Niobium oxycarbonitride, and in particular niobium carbonitride, in which z equals zero, is outstanding for its high critical temperatures, high critical magnetic fields and high critical current densities. Any suitable material (e.g. C, SiC, B, steel) that has the necessary mechanical strength may be used as support fiber material. It serves as high tensile strength matrix and as substrate for a chemical vapor deposition method (CVD=chemical vapor deposition) in which the niobium is deposited as a thin film by reaction of NbCl.sub.5 with H.sub.2 in the presence of the carbon and nitrogen-containing gases. The CVD process is carried out either in a single stage (simultaneous Nb deposition and carbonitration) or in two stages (Nb deposition and carbonitration successively).
Various methods for the deposition of niobium carbonitride or niobium oxycarbonitride are known from German DE-AS No. 28 56 885 and German DE-OS No. 32 28 729. While the method described in DE-AS No. 28 56 885 furnishes in principle superconducting layers which are still too coarse-grained for optimum superconductor properties to be obtained, the necessary fine grain of the superconducting crystals can be obtained by methods according to DE-OS No. 32 28 729. The mean grain size of the B1-structure niobium oxycarbonitride is adjustable between 3 and 50 nm. It has been found, however, that the required and theoretically possible superconduction properties (with regard to current carrying capacity and critical magnetic field) are not yet attainable by the production of superconducting layers using the method according to DE-OS No. 32 28 729.